This invention relates to a thin film magnetic head having an outstanding read ability used for magnetic recording apparatuses such as magnetic disk units and video tape recorders, and to a method of fabricating the thin film magnetic head.
FIG. 1 shows in brief the structure of a conventional thin film magnetic head. The thin film magnetic head is formed of a pair of magnetic cores 1 and 2, a gap forming layer (Al.sub.2 O.sub.3) 3, an insulation layer 4, and a coil 6. In the figure, indicated by 7 is an Al.sub.2 O.sub.3 base film, 8 is a ceramic plate, and 9 is a protection film. For a write operation, a recording current is introduced to the coil 6 so that the magnetic cores 1 and 2 are magnetized, and a signal is recorded on a recording medium (not shown) by the magnetic field which leaks from a gap 10. For a read operation, a magnetic field coming out of the recording medium and passing through the magnetic cores 1 and 2 is detected as a voltage. This magnetic head has read and write abilities using the same magnetic cores 1 and 2. For the magnetic cores, a soft magnetic material with uniaxial anisotropy is generally used because of its high permeability in the high frequency region. In this case, the hard axis of magnetization is oriented to the magnetic path of the magnetic head so that the easy axis of magnetization is substantially orthogonal to the magnetic path. The magnetic core material used currently is a NiFe alloy (Permalloy) with a saturation magnetic flux density of 10,000 G.
In order to increase recording densities of magnetic disk units and the like, it is indispensable to use media with high coercive forces and therefore materials with higher saturation magnetic flux density than Permalloy need to be used for magnetic cores. To meet this requirement, there have been examined amorphous alloys with a saturation magnetic flux density of about 13,000 G, such as CoZrTa, CoHfTa, CoHfTaPd, etc., and crystalline alloys with a saturation magnetic flux density of about 13,000-19,000 G, such as NiFe, CoNiFePd, CoFe, etc., for the magnetic core material.
However, these materials with high saturation magnetic flux density have a large magnetic anisotropy field because of their strong inherent uniaxial anisotropy. The permeability .mu. is represented in terms of the saturation magnetic flux density Bs and magnetic anisotropy field Hk as .mu.=Bs/Hk, and accordingly a large magnetic anisotropy field means a very low permeability. In order to reduce the magnetic anisotropy field through the relaxation of magnetic anisotropy, there has been proposed a method of applying a magnetic field along the magnetization hard axis following the formation of the film, or a method of annealing with the application of a rotating magnetic field, as disclosed in Japanese Patent Publication No. 59-35431, for example. Proposed for the annealing process are 1 a method of magnetic field application along the magnetization hard axis immediately after the formation of the magnetic layer; 2 a method of rotating magnetic field application after the formation of the magnetic layer; 3 a method of annealing without a magnetic field or with a magnetic field applied along the easy axis after the formation of the magnetic layer, and magnetic field application along the magnetization hard axis after the magnetic anisotropy has settled to some extent; and 4 a method of rotating magnetic field application after annealing without a magnetic field or with a magnetic field application along the easy axis after the formation of the magnetic layer.
The pre-annealing along the magnetization easy axis in the method of item 3 is to control the amount of variation of the magnetic anisotropy field during annealing with the application of a magnetic field in the direction of the magnetization hard axis thereby to prevent the rotation of the magnetic anisotropy field so that the direction of the magnetization hard axis is maintained in the magnetic path direction of the magnetic head. The annealing process in the direction of the magnetization easy axis in the method of item 4 is to control the process so that the magnetic anisotropy field does not become too small by annealing in the rotating magnetic field.
Concerning the annealing temperature during the process in the magnetic field, the annealing temperature for reducing a magnetic anisotropy field for the bottom magnetic layer is set higher than the temperature which is experienced in the subsequent processes.
It has been revealed, however, that although thin film magnetic heads fabricated by this method are satisfactory in their write ability, their read ability is inferior as compared with Permalloy. According to the examination conducted by the inventors of the present invention, the magnetic head fabricated by the abovementioned method has the permeability of its magnetic core lowered significantly after the head has been completed as compared with the state immediately after the annealing process. This fact is supposed to be the cause of the unsatisfactory read ability. The reduction of the permeability is possibly caused by the increase of the magnetic anisotropy field, which has been reduced by annealing at the film formation, in the process of terminal attachment after the formation of a film between layers. The change in the magnetic anisotropy field caused by annealing was examined. FIG. 2 shows the change in the magnetic anisotropy field Hk of a CoHfTa film between temperatures 250.degree. C. and 200.degree. C. After the film has been subjected to annealing at 250.degree. C. for 2 hours with the application of a magnetic field along the magnetization easy axis, the film is subjected to the anisotropy reduction process at 200.degree. C. with the application of a magnetic field along the magnetization hard axis, and then the magnetic anisotropy field falls to 7 Oe in 28 hours. However, when the film is annealed again with the application of a magnetic field along the magnetization easy axis, the magnetic anisotropy field rises to 13 Oe in one hour.
The actual head fabricating process includes a number of annealing processes in the absence of a magnetic field, and these processes produce results identical to the case of magnetic field application in the direction of a magnetization easy axis. Namely, it was revealed that the magnetic anisotropy field which has been reduced by the magnetic annealing process increases again during the easy axis annealing of the subsequent head forming process.
A conceivable manner for retaining a small magnetic anisotropy field of a completed magnetic head is to anneal the head during the fabrication process or on completion of fabrication. FIG. 3 shows in brief the profile of temperature in the thin film magnetic head formation process. In the figure, indicated by a to e are positions where annealing of the magnetic core is possible. The figure reveals that in the case of annealing at any position from a to d, the magnetic anisotropy field increases again during such a process as terminal attachment. A conceivable step is the simultaneous annealing for the top and bottom magnetic cores at position e. However, the bottom magnetic core is subjected to annealing for a longer time than the top magnetic core, and therefore it is not possible to provide the same thermal aging for the top and bottom magnetic cores. For this reason, the top and bottom magnetic cores cannot have their magnetic anisotropy field reduced by the same degree. Accordingly, thin film magnetic heads cannot be formed by the conventional technique which simply reduces the magnetic anisotropy field to achieve a quasi-stability.
The foregoing conventional technique involves the problem of degraded read ability of the magnetic head due to the virtual subsidence of the process for increasing the permeability (reduction of the magnetic anisotropy field).
It is an object of this invention to overcome the foregoing prior art deficiencies and to provide a thin film magnetic head having outstanding read and write characteristics and a method of fabricating the head.
In order to achieve the above problem, the inventive thin film magnetic head comprises top and bottom magnetic cores laminated through an insulation layer on a substrate, with both cores having one end in contact with each other and another end forming a magnetic gap, and a conductor layer which winds around the contact area of the top and bottom magnetic cores, wherein at least one of the top and bottom magnetic cores (preferably the top magnetic core) is formed to have its magnetization easy axis virtually orthogonal to the magnetic path direction of the magnetic head, with the direction of the magnetization easy axis being rotated by the magnetic anisotropy field reduction process.
The inventive thin film magnetic head comprises top and bottom magnetic cores laminated through an insulation layer on a substrate, with both cores having one end joining to each other and another end forming a magnetic gap, and a conductor layer which winds around the junction of the top and bottom magnetic cores for a plurality of number of turns, wherein at least one of the top and bottom magnetic cores (preferably the bottom magnetic core) is formed of an amorphous material including cobalt in an amount of 80 atom-% or more (e.g., amorphous alloys CoZrTa, CoHfTa, CoHfTaPd, etc., with a saturation magnetic flux density of about 13,000 G), or a crystalline material including cobalt in an amount of 20 atom-% or more (e.g., NiFe, CoN:FePd, CoFe, etc. with a saturation magnetic flux density of about 13,000-19,000 G), with its magnetization easy axis being oriented to be orthogonal to the magnetic path of the magnetic head and with its magnetization easy axis direction being rotated by 90.degree. using the magnetic annealing process.
The inventive method of fabricating a thin film magnetic head is such that a bottom magnetic layer is formed on a substrate, an insulation layer is formed on the bottom magnitude layer, and a top magnetic layer is formed on the insulation layer, with one end of both magnetic layers joining to each other and another end forming a magnetic gap, and the top and bottom magnetic layers are formed into patterns to form the top and bottom magnetic cores, wherein at least one of the top and bottom magnetic cores is formed with its magnetization easy axis being substantially parallel to the magnetic path direction of the magnetic head, and thereafter its magnetization easy axis is rotated by 90.degree. using a magnetic annealing process so that the magnetization easy axis is orthogonal to the magnetic path direction of the magnetic head, and thereafter it is formed into a magnetic core pattern.
The inventive method of fabricating a thin film magnetic head is such that a bottom magnetic layer is formed on a substrate, an insulation layer is formed on the bottom magnetic layer, and a top magnetic layer is formed on the insulation layer, with one end of both magnetic layers joining to each other and another end forming a magnetic gap, and the top and bottom magnetic layers are formed into patterns to form the top and bottom magnetic cores, wherein at least one of the top and bottom magnetic cores is formed with its magnetization easy axis being parallel to the magnetic path direction of the magnetic head, and thereafter it is annealed with the application of a magnetic field along the magnetization easy axis, and next the magnetization easy axis is rotated by 90.degree. using the magnetic annealing process so that the easy axis is substantially orthogonal to the magnetic path direction of the magnetic head, and thereafter it is formed into a magnetic core pattern. The magnetic annealing process is preferably one of annealing with the application of a rotating ellipsoidal magnetic field, annealing with the application of orthogonal magnetic fields, and annealing with the application of a magnetic field which is substantially orthogonal to the magnetization easy axis. The annealing with the application of a magnetic field along the magnetization easy axis may be replaced with annealing without the application of magnetic field in the direction of the magnetization easy axis.
The inventive method of fabricating a thin film magnetic head comprises a processing step in which a bottom magnetic layer is formed on a substrate, with its magnetization easy axis being oriented along the magnetic path direction of the magnetic head, the magnetization easy axis is rotated by 90.degree. using the magnetic annealing process so that the easy axis is orthogonal to the magnetic path direction of the magnetic head, and thereafter it is formed into a pattern of a bottom magnetic core, and a processing step in which an top magnetic layer is formed on the bottom magnetic layer through an insulation layer, with one end of both magnetic layers being in contact with each other and with another end forming a magnetic gap, and with its magnetization easy axis being oriented to the magnetic path direction of the magnetic head, the magnetization easy axis of the top magnetic layer is rotated by 90.degree. using the magnetic annealing process so that the easy axis is orthogonal to the magnetic path direction of the magnetic head, and thereafter it is formed into a pattern of a top magnetic core.
The problems of the conventional technique is attributed to the difference in the direction of change in the magnetic anisotropy field between the state of anisotropy relaxation and the final state. The most conceivable method of making these trends consistent is the application of a magnetic field along the magnetic path direction of the magnetic head during the whole process except for the formation of the magnetic layers. However, in order to bring the magnetic cores to complete saturation, it is necessary to apply an external magnetic field stronger than the saturation magnetic flux density, and it will be impractical to install a magnetic field application facility which meets this requirement and also to have industrial production output. Moreover, such a magnetic head creates an extreme increase in the magnetic anisotropy field in response to a temperature rise within the range of normal use.
The inventors of this invention have paid attention to the fact that the change in the magnetic anisotropy field is sharp at the beginning and it becomes moderate later, and have found an annealing method which imposes little change in the magnetic anisotropy field in the absence of a magnetic field. This is based on the result of experiment as described below.
FIG. 4 shows the change in the magnetic anisotropy field when a CoHfTa amorphous film is formed and thereafter annealed at 200.degree. C. with the application of a magnetic field along the magnetization hard axis. In the figure, indicated by 12 is the result of annealing in a magnetic field at 250.degree. C. for one hour, and 11 is the result without annealing. The direction of magnetization easy axis rotates by 90.degree. due to annealing, and the magnetic anisotropy field of this case is shown using the negative sign. In the case of 11, the magnetization easy axis is rotated and the magnetic anisotropy field rises beyond 10 Oe by annealing for one hour, and the rate of change in the magnetic anisotropy field falls below 0.3 Oe/h at a point of 5-hour annealing. On the other hand, in the case of 12, the magnetization easy axis is rotated by 90.degree. using the magnetic annealing of one hour and the magnetic anisotropy field is as small as 3 Oe, and the rate of change in the magnetic anisotropy field falls below 0.7 Oe/h. When attention is paid to the fact that the film is annealed with the application of a magnetic field along the magnetization easy axis for a portion of a negative magnetic anisotropy field and that the rate of change of the magnetic anisotropy field is small in this portion, it is concluded that, since the annealing with the application of a magnetic field along the magnetization easy axis is comparable to the annealing in the absence of magnetic field, there can be a stable state with a small magnetic anisotropy field even in the absence of the external magnetic field.